If you want to reduce weight there is no way but diet, sorry.
Exercise will make you more healthy and will shape your body better (and is very recommended), but in the end the loss of weight is very low.
Also don't bother with any lo carb or low fat or whatever new hip diet. In the end it comes down to energy eaten and energy used. If you use more then you eat you will loose weight.
Regarding what AD said about the metabolism reducing itself to prevent further loss - unfortunately this is true. So either you settle for a very slow weight loss (and a high degree of exercise) to avoid this mechanism OR if you have a very high willpower (sorry to tell you, but the wonder drug just doesn't exist - weight loss is foremost a brain thing) you actually reduce you calory input by an extend that even that low metabolism won't get enough calories. Be warned however that at least the second option should not be done without regular checkups and quite health meal selection or you will get sick.